Vehicle control apparatus

ABSTRACT

A vehicle control apparatus includes a steering torque sensor (1) for sensing a steering torque, a motor (3) for generating a steering assisting force, a CPU (22) for determining a motor drive direction based on at least the steering force and a motor drive direction restricting circuit (25) for restricting the drive direction of the motor (3) determined by the CPU (22) based on a steering force determination level as a motor drive direction determination criterion and the steering force, and the steering force determination level is changeable. With this arrangement, there is provided the vehicle control apparatus with safety and reliability by which the motor can be controlled with redundancy, the steering force determination level does not require such accuracy as to use pinpoint accuracy and further even if an abnormal state is caused in a motor output when a steering wheel is released from a hand and a steering torque exceeding the steering force determination level is generated, the steering force determination level is instantly changed to thereby restrict a motor drive direction so that the self-turn of the steering wheel is prevented.

This is a divisional of application Ser. No. 08/615,462 filed Mar. 14,1996, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle control apparatus having amotor drive direction restricting means for restricting a motor drivedirection, and more specifically, to an electrically-driven powersteering control apparatus for assisting and urging steering operation.

2. Description of the Related Art

Conventionally, a method of preventing the rotation of a motor in anunexpected direction caused by the abnormal state and the like of a CPUis proposed by Japanese Patent Publication No. 6-51475 filed by theinventors. This method is realized by an electrically-driven powersteering apparatus for assisting and urging steering operationcomprising a microcomputer for outputting a motor rightward drive signaland leftward drive signal based on the output from a steering torquesensor, a motor drive direction determination circuit for outputting arightward drive signal and leftward control signal from the output of asteering torque sensor provided with a motor control circuit unit, andan AND circuit for outputting, when the output from the microcomputercoincides with the output from the motor drive discrimination circuit, asignal for driving a motor in the direction of the coincidence.

FIG. 29 is a circuit diagram showing a motor drive directiondiscrimination circuit (torque direction discrimination circuit) in theconventional electrically-driven power steering control apparatusdisclosed in, for example, Japanese Patent Publication No. 6-51475.

In the drawing, a torque signal is input to the inverting input terminalof a comparator CMP1 and the non-inverting input terminal of acomparator CMP2. Further, a first fixed reference voltage E1 and asecond fixed reference voltage E2 which are obtained by dividing a powersupply voltage Vt by resistors R1, R2 and R3 are input to thenon-inverting input terminal of the comparator CMP1 and the invertinginput terminal of the comparator CMP2, respectively.

Next, the operation of the circuit will be described.

The comparator CMP1 compares the torque signal t with the referencevoltage E1 and when t>E1, the output Ex1 of the comparator CMP1 is at anL level. Whereas, when t<E1, the output Ex1 is at an H level.

Likewise, the comparator CMP2 compares the torque signal t with thereference voltage E2, and when t>E2, the output Ey1 of the comparatorCMP2 is at the H level. Whereas, when t<E2, the output Ey1 is at the Llevel.

When the output Ex1 of the comparator CMP1 is at the H level, arightward output is prohibited. Likewise, when the output Ey1 of thecomparator CMP2 is at the H level, a leftward output is prohibited.

FIG. 30 is a view explaining a motor output and the operation of thetorque direction discrimination circuit.

In the figure, a relationship T4<T1<T0<T2<T3 is established in torquesfrom T0 to T4. The torque signal t<T0 results in a leftward torque, thetorque signal t>T0 results in a rightward torque and the torque signalt=T0 results in neutral. When the torque signal t is between T2 and T3or between T4 and T1, a value proportional to the torque signal t isdetermined as the motor output, when the torque signal t is equal to orless than T4 or larger than T3, the motor output is fixed to the maximumvalue Imax of a motor output current and when the torque signal t isbetween T1 and T2, the motor output becomes zero. Further, therelationship between torque determination reference values E1_(T) andE2_(T) corresponding to the reference voltages E1 and E2 of the torquedirection discrimination circuit, respectively and the torque signals T1and T2 are set to T1<E2_(T) <E1_(T) <T2. With this arrangement, when atorque is equal to or less than the reference value E1_(T), motorrightward drive is prohibited and when a torque is larger than thereference value E2_(T), motor leftward drive is prohibited. Further,when a torque is between the reference value E1_(T) and E2_(T), both ofrightward and leftward motor drive are prohibited.

The substitution of the non-inverting input terminals for the invertinginput terminals of the comparators CMP1 and CMP2 of the torque directiondiscrimination circuit results in a torque direction discriminationcircuit or a motor drive direction discrimination circuit as shown inFIG. 31.

In the drawing, the torque signal t is input to the non-inverting inputterminal of a comparator CMP3 and the inverting input terminal of acomparator CMP4. Further, a third fixed reference voltage E3 and afourth fixed reference voltage E4 which are obtained by diving the powersupply voltage Vt by the resistors R1, R2 and R3 are input to theinverting input terminal of the comparator CMP3 and the non-invertinginput terminal of the comparator CMP4, respectively.

Next, the operation of the circuit will be described.

The comparator CMP3 compares the torque signal t with the referencevoltage E3 and when t>E3, the output Ex2 of the comparator CMP3 is at anH level. Whereas, when t<E3, the output Ex2 is at an L level. Likewise,the comparator CMP4 compares the torque signal t with the referencevoltage E4 and when t>E4, the output Ey2 of the comparator CMP4 is atthe L level. Whereas, when t<E4, the output Ey2 is at the H level.

When the output Ex2 of the comparator CMP3 is at the L level, a leftwardoutput is permitted. Likewise, when the output Ey2 of the comparatorCMP4 is at the L level, a rightward output is permitted.

FIG. 32 is a view explaining a motor output and the operation of thetorque direction discrimination circuit.

In the drawing, a relationship T4<T<T0<T2<T3 is established in torquesfrom T0 to T4. The torque signal t<T0 results in a leftward torque, thetorque signal t>T0 results in a rightward torque and the torque signalt=T0 results in neutral. When the torque signal t is between T2 and T3or between T4 and T1, a value proportional to the torque signal t isdetermined as the motor output, when the torque signal t is equal to orless than T4 or larger than T3, the motor output is fixed to the maximumvalue Imax of a motor output current and when the torque signal t isbetween T1 and T2, the motor output becomes zero. Further, therelationship between torque determination reference values E3_(T) andE4_(T) corresponding to the reference voltages E3 and E4 of the torquedirection discrimination circuit, respectively and the torque signals T1and T2 is set to E4_(T) <T1<T2<E3_(T). With this arrangement, when atorque is equal to or less than E3_(T), motor leftward drive ispermitted and when a torque is larger than E4_(T), motor rightward driveis permitted. Further, when a torque is between the reference valueE3_(T) and E4_(T), both of rightward and leftward motor drive arepermitted.

Since the conventional apparatus is arranged as described above, it hasthe following problem.

That is, the torque determination reference values E1_(T) to E4_(T) arefixed in the conventional apparatus. As a result, when the motor drivedirection determination level (torque determination reference value) ofa steering torque as the torque signal t is represented by E1_(T),E2_(T) (E2_(T) <E1_(T)), motor drive direction restricting meansincluding the torque direction discrimination circuit prohibits motorrightward drive when the steering torque t satisfies t<E2_(T) andprohibits motor leftward drive when the steering torque satisfies E1_(T)<t. Further, when the steering torque t satisfies E2_(T) ≦t≦E1_(T),there are two methods of permitting motor drive (hereinafter, referredto as neutral permission) and prohibiting motor drive (hereinafter,referred to as neutral prohibition). The neutral permission hascharacteristics shown in FIG. 32 and the neutral prohibition hascharacteristics shown in FIG. 30.

In the neutral prohibition, even if a steering wheel is released from ahand in an abnormal motor output (steering torque is neutral), sincemotor drive is prohibited, inconvenience such as the self-turn(unintentional rotation) of the steering wheel and the like is notcaused and safety is secured. However, when a steering torque is withinthe neutral determination region (for example, when the steering wheelis released), since the motor drive direction restricting meansprohibits motor drive, the motor cannot be controlled. That is, sincethere is a problem that a motor control cannot be executed in theneutral prohibition, the motor cannot be controlled with redundancy.

Further, the motor drive direction determination levels E1_(T), E2_(T)must be set to T1<E2_(T) <E1_(T) <T2 From FIG. 30. This is because thatwhen the motor drive direction determination levels E1_(T), E2_(T) areset to E2_(T) <T1<T<E1_(T), since a motor output is prohibited by themotor drive direction restricting means between E2_(T) and T1 andbetween T2 and E1_(T), there is a problem that a motor current causeshunting. To cope with this problem, when the motor drive directiondetermination level is composed of an H/W, resistors and the likerequire pinpoint accuracy, and thus the cost of the H/W composed of theresistors and the like of pinpoint accuracy is increased.

Furthermore, since motor drive is prohibited when a steering torque iswithin the neutral determination region, there is a lack of an assistingforce when the motor is driven so that when the steering wheel states tobe cut, it is felt heavy. That is, the motor drive prohibition adverselyaffects the feeling in steering operation when a torque is neutral.

In addition, in the neutral permission, even if a steering torque iswithin the neutral determination region (between T1 and T2), a motor canbe driven and thus the motor control can be executed with redundancy.However, since the motor can be driven even if a steering torque iswithin the neutral determination region, when the steering wheel isreleased from a hand in an abnormal motor output, there is possibilitythat the steering wheel turns by itself. To avoid the occurrence of asteering wheel self-turn mode and the like, the neutral permissionregion is conventionally set to a narrow region, wherein a problem thatthe neutral permission region cannot be set in a wide range.

An object of the present invention made to overcome the above problemsis to provide a vehicle control apparatus having both of the redundancyof a motor control as an advantage of neutral permission and the safetyas an advantage of neutral prohibition by changing a steering forcedetermination level and further capable of increasing the range of aneutral permission region and driving a motor even in a neutralprohibition region.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided avehicle control apparatus which comprises steering force sensing meansfor sensing a steering force, a motor for generating a steeringassisting force, motor drive means for determining the drive directionof the motor based on at least the steering force, and motor drivedirection restricting means for restricting the drive direction of themotor determined by the motor drive means based on a steering forcedetermination level as the drive direction determination criterion ofthe motor and the steering force, wherein the steering forcedetermination level is changeable.

According to this arrangement, there are advantages that a neutralpermission region can be set in a wide range in a normal motor output,the motor can be controlled with redundancy due to the neutralpermission region capable of being set to the wide range, and furthersince the steering force determination level is changed when the motordrive means is in an abnormal state, the steering force determinationlevel does not require pinpoint accuracy. Further, when a steeringtorque exceeds the steering force determination level in an abnormalmotor output, the steering force determination level is instantlychanged to restrict a motor drive direction to the motor drive directiondetermined by a steering torque. As a result, even if an abnormal motoroutput is generated and thus a steering torque exceeding the steeringforce determination level is generated when a steering wheel is releasedfrom a hand, the self-turn of the steering wheel can be prevented byrestricting the motor drive direction by the instant change of thesteering force determination level, whereby there is an advantage that asystem with safety and reliability can be provided.

In one form of the invention, the steering force determination levelchanges with a predetermined delay element with respect to the change ofstate of the motor drive means, and it is kept at a predetermined levelin accordance with the state of the motor drive means.

According to this arrangement, a motor drive prohibition region can beset in correspondence to the state of the motor drive means. That is,since a direction in which the motor can be driven is set with respectto the state of the motor drive means and the motor is permitted to bedriven only when a motor drive direction and a steering torque coincidewith each other and when they do not coincide with each other, the motoris prohibited to be driven, there is an advantage that a system withsafety and reliability can be provided. Further, since the delay elementis provided with the change of the steering force determination level,such a control as to drive the motor in a direction opposite to asteering torque can be carried out by adjusting the time constant of thedelay element while the steering force determination level changes. Thatis, there is an advantage that a motor is controlled with redundancy.Further, since the steering force determination level is changeddepending upon the state of the motor drive means, the restrictionagainst a motor drive direction is kept while the motor drive meanscarries out a motor output and thus when the restriction against themotor drive direction being kept is released, the motor output isstopped. Thus, there is an advantage that when the restriction effectedby the motor drive direction restricting means is released, the motor isnot driven and safety is secured.

In another form of the invention, the steering force determination levelchanges with a predetermined delay element with respect to the change ofstate of the motor drive means or the change of state of the motor drivedirection restricting means, and the steering force determination levelat the time when motor drive is output by the motor drive means or whena motor drive direction is restricted by the motor drive directionrestricting means is kept until the state of the motor drive means andthe state of the motor drive direction restricting means are made to amotor drive stop state and a motor drive direction restriction releasestate respectively.

According to this arrangement, when the motor is driven in an abnormaldirection, since a motor drive prohibition region can be instantly setdepending upon the state of the motor drive direction restricting meansand further a restricted motor drive direction is not released untilsafety is confirmed by the state of the motor drive means and the stateof the motor drive direction restricting means, there is an advantagethat a system with safety and reliability can be provided. When themotor is driven in an abnormal direction, a motor drive direction isrestricted by the motor drive direction restricting means and thesteering force determination level is changed by the output from themotor drive direction restricting means, there is an advantage that whenthe motor is driven in an abnormal direction, a motor drive directioncan be instantly restricted. Further, since the steering forcedetermination level is also changed by the state of the motor drivemeans, there is an advantage that a motor drive prohibition region isset in accordance with a motor drive direction while a motor drive isoutput, that is, the motor drive prohibition region is kept until themotor drive output by the motor drive means is stopped.

In a further form of the invention, the steering force determinationlevel changes with a predetermined delay element with respect to thechange of state of the motor drive means, and the changing speed of thesteering force determination level at the time when the motor drivemeans changes from a stop state to a drive state is made slower than thechanging speed thereof when the motor drive means changes from the drivestate to the stop state.

According to this arrangement, there is an advantage that the motor canbe driven in a direction where the polarity of motor drive does notcoincide with the polarity of a motor drive direction. Further, there isan advantage that the steering force determination level can beprevented from being made unstable by setting a different value to thetime constant of the delay element when the motor is driven and when itis stopped. Further, the time constant which is changed by the stop ofthe motor is set faster than the time constant which is changed by thedrive of the motor so that the steering force determination levelinstantly returns to the level at the time the motor drive is stopped.Thus, there is an advantage that when the motor is repeatedly driven andstopped, the steering force determination level instantly returns to thelevel at the time the motor drive is stopped, the steering forcedetermination level is made stable and further the motor drive directionrestricting means is difficult to cause malfunction.

In a still further form of the invention, the steering forcedetermination level changes with a predetermined delay element withrespect to the change of state of the motor drive means or the change ofstate of the motor drive direction restricting means and the changingspeed of the steering force determination level due to the change ofstate of the motor drive direction restricting means is made faster thanthe changing speed of the steering force determination level due to thechange of state of the motor drive means.

According to this arrangement, there is an advantage that when a motordrive direction is restricted by the motor drive direction restrictingmeans, the time constant of the delay element is changed and a directionin which the motor can be driven is restricted by instantly changing thesteering force determination level, whereby the safety and reliabilityof the system is improved.

In a yet further form of the invention, the steering force determinationlevel changes exceeding a neutral level when the motor drive meanschanges to a motor drive state or when the motor drive directionrestricting means changes to a motor drive direction restricting state.

According to this arrangement, a direction in which the motor can bedriven is restricted to one direction, that is, one direction includinga neutral position is set as a motor drive restricting region by thesteering force determination level. As a result, the motor can be drivenwhen the polarity of a motor drive direction and the polarity of asteering torque coincide with each other as well as the absolute valueof the steering torque changes exceeding the neutral position andbecomes larger than the steering force determination level, thus even ifthe steering wheel is released from a hand (a steering torque becomesneutral) when a motor output is in an abnormal state, inconvenience suchas the self-turn of the steering wheel and the like (the motor drivedirection is restricted because when the steering wheel is released, thepolarity of the steering torque caused by the motor drive does notcoincide with the polarity of the motor drive direction), whereby asystem with safety and reliability can be provided.

In a still another form of the invention, the steering forcedetermination level changes with respect to at least the state of themotor drive means or the state of the motor drive direction restrictingmeans, and when said motor is not driven, the steering forcedetermination level is set to the level which is taken when restrictionby the motor drive direction restricting means is released.

According to this arrangement, when the motor is not driven, therestriction against a motor drive direction is released and this is alsoapplicable to a direction in which the motor is not driven in the sameway, and, for example, when the motor is driven rightward, the steeringforce determination level is set to a level by which the restrictionagainst a motor rightward drive direction is released and a sufficientassisting force can be obtained when the steering wheel starts to be cutin combination with the delay of change of the steering forcedetermination level when the motor is driven. Thus, there is anadvantage that the motor can be smoothly driven an adverse affect tosteering feeling can be prevented.

In a still another form of the invention, the steering forcedetermination level changes with a delay element with respect to atleast the state of the motor drive means or the state of the motor drivedirection restricting means, and the steering force determination levelat the time when the restriction against a motor drive direction made bythe motor drive direction restricting means is released is made largerthan a predetermined value.

According to this arrangement, a motor drive direction can be preventedfrom being restricted by the motor drive direction restricting meanswhich is operated by a steering torque caused by the control and thelike for driving the motor in a direction where the polarity of a motordrive direction does not coincide with the polarity of a steeringtorque. Thus, there is an advantage that the motor can be controlledwith redundancy.

In a still another form of the invention, there is provided a vehiclespeed sensing means for sensing a vehicle speed, wherein the steeringforce determination level changes with respect to at least the state ofthe motor drive means, or the state of the motor drive directionrestricting means and the steering force determination level at the timewhen the restriction against a motor drive direction made by the motordrive direction restricting means is released is set with respect to thevehicle speed.

According to this arrangement, there is an advantage that malfunction ofthe motor drive direction restricting means caused when the steeringwheel is operated at a high speed can be suppressed by that when amaximum torque generated at the time the steering wheel is operated atthe high speed is larger than a predetermined vehicle speed within asteering torque input range, the steering force determination level isset larger than the maximum torque.

In a still another form of the invention, there is provided a clutch forcoupling the motor with a steering system, wherein the steering forcedetermination level changes with respect to at least the state of themotor drive means or the state of the motor drive direction restrictingmeans, and when the clutch is disengaged, the restriction made by themotor drive direction restricting means is released.

According to this arrangement, there is an advantage that an abnormalstate such as motor lock and the like can be checked by driving themotor, and since the motor is driven when a clutch is disengaged, amotor assisting force is not transmitted to the steering wheel andsafety is secured.

In a still another form of the invention, the steering forcedetermination level changes with respect to at least the state of themotor drive means or the state of the motor drive direction restrictingmeans, and it is set within the input possible range of the steeringforce sensing means.

According to this arrangement, there is an advantage that when anabnormal steering force is generated by an abnormal motor output, themotor drive direction restricting means is operated to restrict a motordrive direction, whereby the occurrence of the self-turn of the steeringwheel and the like can be prevented and thus safety and reliability isimproved.

In a still another form of the invention, the steering forcedetermination level changes with respect to at least the state of themotor drive means or the state of the motor drive direction restrictingmeans, and motor drive is prohibited when the restriction against amotor drive direction made by the motor drive direction restrictingmeans continues longer than a predetermined period of time at the timethe steering force has a value equal to or less than a predeterminedvalue.

According to this arrangement, there is an advantage that when a motordrive direction is restricted by the motor drive direction restrictingmeans, the failure of the motor drive direction restricting means, motordrive means and the like can be sensed and thus the safety andreliability of the system is improved.

In a still another form of the invention, the steering forcedetermination level changes with respect to at least the state of themotor drive means or the state of the motor drive direction restrictingmeans, and the operation of the motor drive direction restricting meansis estimated from the state of the motor drive means or the steeringforce and it is compared with the operation of the motor drive directionrestricting means, and when the incoincidence of them continues longerthan a predetermined period of time, motor drive is prohibited.

According to this arrangement, there is an advantage that since theabnormal state of the motor drive direction restricting means, motordrive means, steering force sensing means and the like can be sensedregardless of the state of the motor drive torque restricting means andthus the reliability of the system is improved.

According to another aspect of the present invention, there is provideda vehicle control apparatus which comprises steering force sensing meansfor sensing a steering force, a motor for generating a steeringassisting force, a target current determination means connected to thesteering force sensing means for determining a target motor currentbased on at least the steering force, current sensing means for sensinga current flowing to the motor, motor drive means connected to thesteering force sensing means for determining a motor drive directionbased on at least the steering force, and motor drive directionrestricting means connected to the steering force sensing means and themotor drive means and changing with respect to at least the state of themotor drive means for restricting the motor drive direction based on asteering force determination level as a drive direction determinationcriterion of the motor and the steering force, wherein a feedbackcontrol is carried out so that a current flowing to the motor becomesthe target current determined by the target current determination meansand when a motor drive direction is restricted by the motor drivedirection restricting means, a motor output is stopped and the targetmotor current is set to zero.

According to this arrangement, there is an advantage that the occurrenceof an abnormal state in a motor control system can be prevented andfurther there can be solved the inconvenience of occurrence of anabnormal state such as shock and the like to the steering feeling of thesteering wheel due to the suspension of the flow of a large current whenthe restriction against a motor drive direction made by the motor drivedirection restricting means is released.

According to a further aspect of the present invention, there isprovided a vehicle control apparatus which comprises steering forcesensing means for sensing a steering force, a motor for generating asteering assisting force, a first microcomputer connected to thesteering force sensing means for controlling the motor by determining amotor drive direction based on the steering force, and a secondmicrocomputer connected to the steering force sensing means and thefirst microcomputer for restricting the drive of the motor bydetermining a motor drive restricting direction based on the motor drivedirection of the first microcomputer and at least the steering force,wherein the second microcomputer includes a motor drive restrictingmeans for changing a steering force determination level in accordancewith the motor drive direction of the first microcomputer as well asdetermining the motor drive restricting direction in accordance with theresult of comparison of the steering force with the steering forcedetermination level, and the motor drive restricting means restricts themotor drive restricting direction in accordance with the result ofcomparison of the steering force determination level which constitutes apair with a motor drive direction determined based on the steeringtorque and the steering force.

According to this arrangement, there is an advantage that since a motordrive direction can be restricted by comparing only the steering forcedetermination level corresponding to a motor drive direction with asteering force and motor drive can be restricted only in a directioncorresponding to the polarity of the steering force, thus excellentsteering feeling can be provided by removing an adverse affect appliedto steering feeing by the motor drive direction restricting means andthe safety and reliability of the system is improved.

In a still another form of the invention, phase compensation means isinterposed between the steering force sensing means and the motor drivedirection restricting means.

According to this invention, there is an advantage that since the phasecompensation means is interposed between the steering force sensingmeans and the motor drive direction restricting means, the hunting of amotor current can be suppressed which is caused a difference between theresponse speed of the control system and the response speed of the motordrive direction restricting means.

In a still another form of the invention, the motor drive means includesa bridge circuit composed of at least four transistors and the motordrive direction restricting means restricts operation with respect to apair of the transistors of the bridge circuit.

According to this arrangement, there is an advantage that the occurrenceof a motor regenerative current is prevented to thereby reduce adifference between a right steering torque and a left steering torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the arrangement of an embodiment 1 ofa vehicle control apparatus according to the present invention;

FIG. 2 is a block diagram showing the function of the embodiment 1 ofthe vehicle control apparatus according to the present invention;

FIG. 3 is a circuit diagram showing a main portion of the embodiment 1of the vehicle control apparatus according to the present invention;

FIG. 4 a circuit diagram showing another main portion of the embodiment1 of the vehicle control apparatus according to the present invention;

FIG. 5 is a view explaining the operation of the embodiment 1 of thevehicle control apparatus according to the present invention;

FIG. 6 is a block diagram showing the arrangement of an embodiment 2 ofthe vehicle control apparatus according to the present invention;

FIG. 7 is a circuit diagram showing a main portion of the embodiment 2of the vehicle control apparatus according to the present invention;

FIG. 8 is a view explaining the operation of the embodiment 2 of thevehicle control apparatus according to the present invention;

FIG. 9 is a block diagram showing the arrangement of an embodiment 3 ofthe vehicle control apparatus according to the present invention;

FIG. 10 is a view explaining the operation of the embodiment 3 of thevehicle control apparatus according to the present invention;

FIG. 11 a circuit diagram showing a main portion of an embodiment 4 ofthe vehicle control apparatus according to the present invention;

FIG. 12 is a view explaining the operation of the embodiment 4 of thevehicle control apparatus according to the present invention;

FIG. 13 is a view explaining the operation of the embodiment 4 of thevehicle control apparatus according to the present invention;

FIG. 14 is a view explaining the operation of an embodiment 5 of thevehicle control apparatus according to the present invention;

FIG. 15 is a block diagram showing the arrangement of an embodiment 6 ofthe vehicle control apparatus according to the present invention;

FIG. 16 is a block diagram showing the function of the embodiment 6 ofthe vehicle control apparatus according to the present invention;

FIG. 17 is a view explaining the operation of an embodiment 7 of thevehicle control apparatus according to the present invention;

FIG. 18 is a block diagram showing the arrangement of an embodiment 8 ofthe vehicle control apparatus according to the present invention;

FIG. 19 is a flowchart explaining the operation of the embodiment 8 ofthe vehicle control apparatus according to the present invention;

FIG. 20 is a block diagram showing the function of a main portion of anembodiment 9 of the vehicle control apparatus according to the presentinvention;

FIG. 21 is a flowchart explaining the operation of the embodiment 9 ofthe vehicle control apparatus according to the present invention;

FIG. 22 is a block diagram showing the arrangement of an embodiment 10of the vehicle control apparatus according to the present invention;

FIG. 23 is a flowchart explaining the operation of the embodiment 10 ofthe vehicle control apparatus according to the present invention;

FIG. 24 is a block diagram showing the arrangement of an embodiment 11of the vehicle control apparatus according to the present invention;

FIG. 25 is a flowchart explaining the operation of the embodiment 11 ofthe vehicle control apparatus according to the present invention;

FIG. 26 is a flowchart explaining the operation of an embodiment 12 ofthe vehicle control apparatus according to the present invention;

FIG. 27 is a block diagram showing the arrangement of an embodiment 13of the vehicle control apparatus according to the present invention;

FIG. 28 is a flowchart explaining the operation of the embodiment 13 ofthe vehicle control apparatus according to the present invention;

FIG. 29 is a circuit diagram showing a specific example of aconventional motor drive direction restricting means;

FIG. 30 is a view explaining the operation of FIG. 29;

FIG. 31 is a circuit diagram showing a specific example of theconventional motor drive direction restricting means; and

FIG. 32 is a view explaining the operation of FIG. 31;

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings with respect to an example in which thepresent invention is applied to an electrically-driven power steeringcontrol apparatus as an example.

Embodiment 1

FIG. 1 is a block diagram showing the arrangement of an embodiment 1 ofthe present invention.

In the drawing, a vehicle control apparatus includes a steering torquesensor 1 as steering force sensing means for sensing a twisting forceapplied to a steering system, a controller 2 for an electrically-drivenpower steering system and a motor 3 connected to the steering system.

Usually, the electrically-driven power steering system senses a steeringforce by the steering torque sensor 1 and the controller 2 determines amotor current corresponding to the steering force and drives the motor3. The motor 3 generates an assisting force corresponding to the currentflowing to the motor 3 to assist steering operation.

The controller 2 is composed of a torque signal input I/F circuit 21 towhich an output signal is supplied from the steering torque sensor 1, amicrocomputer 22 (hereinafter, referred to as CPU 22) which is suppliedwith a torque signal as an output signal from the torque signal inputI/F circuit 21 and outputs a signal for driving the motor 3 according tothe torque signal, a motor rightward drive output I/F circuit 23 andmotor leftward drive output I/F circuit 24 for outputting a motorrightward drive signal and motor leftward drive signal, respectivelybased on the motor drive signal from the CPU 22, a motor drive directionrestricting circuit 25 as motor drive direction control means forrestricting a motor drive direction based on the output signal from thesteering torque sensor 1, AND circuits 26a, 26b for determining whetheror not the output from the motor rightward drive output I/F circuit 23coincides with the output from the motor drive direction restrictingcircuit 25 and outputting a motor drive prohibition signal when they donot coincide with each other, AND circuits 26c, 26d for determiningwhether or not the output from the motor leftward drive output I/Fcircuit 24 coincides with the output from the motor drive directionrestricting circuit 25 and outputting a motor drive prohibition signalwhen they do not coincide with each other in the same manner, a motordrive circuit 27 for driving the motor 3 in response to the outputsignals from the AND circuits 26a, 26b, 26c and 26d and a motor currentsensing circuit 28 connected to the motor drive circuit 27 for sensingthe current flowing to the motor 3.

The motor drive direction restricting circuit 25 in the controller 2inputs the signal from the steering torque sensor 1 to a rightwardtorque comparison unit 251 and a leftward torque comparison unit 252.The rightward torque comparison unit 251 compares the rightward steeringforce determination level determined by a rightward steering forcediscrimination level determination unit 253 with the signal from thesteering torque sensor 1 and restricts motor rightward drive by theresult of comparison. Further, the leftward torque comparison unit 252compares the leftward steering force determination level determined by aleftward steering force discrimination level determination unit 254 withthe signal from the steering torque sensor 1 and restricts motorleftward drive by the result of comparison.

The rightward steering force determination level to be determined by therightward steering force discrimination level determination unit 253 isdetermined based on the result of the output from the rightward torquecomparison unit 251. Further, the leftward steering force determinationlevel to be determined by the leftward steering force discriminationlevel determination unit 254 is determined based on the result of theoutput from the leftward torque comparison unit 252.

FIG. 2 shows an example of the functional block diagram of the CPU 22.The CPU 22 is composed of phase compensation means 221 to which theoutput from the steering torque sensor 1 is supplied through the torquesignal input I/F circuit 21 (FIG. 1), target current determination means222 to which the output from the phase compensation means 221 issupplied, motor current sensing means 223 to which the output from themotor current sensing circuit 28 (FIG. 1) is supplied and motor drivemeans 224 to which the added output of the output from the targetcurrent determination means 222 and the output from the motor currentsensing means 223 is supplied.

The phase of the steering torque sensed by the steering torque sensor 1is compensated by the phase compensation means 221 in the CPU 22 and thetarget current determination means 222 determines a target current usingthe phase-compensated torque value. The motor current sensing means 223senses the current flowing to the motor 3. Then, a deviation between thetarget current value determined by the target current determinationmeans 222 and the motor current sensed by the motor current sensingmeans 223 is determined and the motor drive means 224 outputs a motordrive signal based on the deviation. The motor drive signal is used asthe motor drive signal of the CPU 22. The motor 3 is driven in responseto a signal obtained by ANDing the motor drive signal from the CPU 22and the motor drive signal from the motor drive direction restrictingcircuit 25 by the AND circuit 26.

Next, overall operation will be described.

When the output from the steering torque sensor 1 is supplied to the CPU22 through the torque signal input I/F circuit 21, the CPU 22 determinesa motor drive direction and a target motor current value based on thetorque signal from the torque signal input I/F circuit 21. When arightward torque is generated, the motor drive direction is a rightdirection and when a leftward torque is generated, the motor drivedirection is a left direction.

Further, the CPU 22 determines a motor output value from a differencebetween the motor current value sensed by the motor current sensingcircuit 28 and the target motor current value and outputs the motoroutput value to the motor rightward drive output I/F circuit 23 or motorleftward drive output I/F circuit 24.

When a motor rightward drive signal and the motor output value are inputto the motor rightward drive output I/F circuit 23 from the CPU 22, themotor rightward drive output I/F circuit 23 outputs a motor rightwarddrive output signal to the AND circuits 26a and 26b.

Likewise, when a motor leftward drive signal and the motor output valueare input to the motor leftward drive output I/F circuit 24 from the CPU22, the motor leftward drive output I/F circuit 24 outputs a motorleftward drive output signal to the AND circuits 26c and 26d.

The motor drive direction restricting circuit 25 restricts a motor drivedirection based on the output from the steering torque sensor 1regardless of the processing executed by the CPU 22.

FIG. 3 is a circuit diagram showing an example of the specific circuitarrangement of the motor drive direction restricting circuit 25.

In the drawing, CMP11 denotes a comparator constituting the rightwardtorque comparison unit 251 and having a non-inverting input terminalconnected to the node where voltage dividing resistors R11 and R12,which are connected between a power supply terminal Vcc and the ground,are connected and an inverting input terminal to which a steering torqueis supplied from the steering torque sensor 1. A plurality oftransistors TR1 and TR2 are connected between the non-inverting inputterminal and output terminal of the comparator CMP11. The transistor TR1has an emitter connected to the power supply terminal Vcc, a collectorconnected to the non-inverting input terminal of the comparator CMP11through the resistor R13 and a base connected to the collector of thetransistor TR2 through a resistor. The transistor TR2 has an emittergrounded and a base connected to the output terminal of the comparatorCMP11 through a resistor. The components other than the comparator CMP11constitutes the rightward steering force discrimination leveldetermination unit 253.

Likewise, CMP12 denotes a comparator constituting the leftward torquecomparison unit 252 and having an inverting input terminal connected tothe node where voltage dividing resistors R14 and R15, which areconnected between the power supply terminal Vcc and the ground, areconnected and a non-inverting input terminal to which the steeringtorque is supplied from the steering torque sensor 1. A transistor TR3is connected between the inverting input terminal and output terminal ofthe comparator CMP12. The transistor TR3 has an emitter grounded, acollector connected to the inverting input terminal of the comparatorCMP12 through a resistor R16 and a base connected to the output terminalof the comparator CMP12 through a resistor. The components other thanthe comparator CMP12 constitutes the leftward steering forcediscrimination level determination unit 254.

The comparator CMP11 compares the level of the non-inverting inputterminal with the level of the inverting input terminal. That is, thecomparator CMP11 compares the output from the rightward steering forcediscrimination level determination unit 253 with the level of the outputfrom the steering torque sensor 1, and when the level of thenon-inverting input terminal is larger than the level of the invertinginput terminal, the comparator CMP11 outputs a high level "H", whereaswhen the level of the non-inverting input terminal is smaller than thelevel of the inverting input terminal, it outputs a low level "L".

When the output from the comparator CMP11 is at the high level "H", themotor rightward drive is prohibited. At the time, since the transistorsTR2 and TR1 are turned on together, the level of the non-inverting inputterminal of the comparator CMP11, that is, the steering forcedetermination value V4 (refer to FIG. 5) supplied from the rightwardsteering force discrimination level determination unit 253 to thecomparator CMP11 is determined by the resistors R11, R12 and R13.

When it is assumed that the resistance values of the resistors and thepower supply voltage of the power supply terminal are represented by thesame numerals as these components, the steering force determinationvalue V4 is represented by the following formula.

    V4=R12/[{R11·R13/(R11+R13)}+R12]×Vcc        (1)

When the output from the comparator CMP11 is at the low level "L", themotor rightward drive is permitted. At the time, since the transistorsTR2 and TR1 are turned off together, the level of the non-invertinginput terminal of the comparator CMP11, that is, the steering forcedetermination value V2 (refer to FIG. 5) supplied from the rightwardsteering force discrimination level determination unit 253 to thecomparator CMP11 is determined by the resistors R11 and R12. That is,the steering force determination value V2 is represented by thefollowing formula.

    V2=R12/(R11+R12)×Vcc                                 (2)

The comparator CMP12 compares the level of the inverting input terminalwith the level of the non-inverting input terminal. That is, thecomparator CMP12 compares the output from the leftward steering forcediscrimination level determination unit 254 with the level of the outputfrom the steering torque sensor 1, and when the level of the invertinginput terminal is larger than the level of the non-inverting inputterminal, the comparator CMP12 outputs the low level "L", whereas whenthe level of the inverting input terminal is smaller than the level ofthe non-inverting input terminal, it outputs the high level "H".

When the output from the comparator CMP12 is at the high level "H",motor leftward drive is prohibited. At the time, since the transistorTR3 is turned on, the level of the non-inverting input of the comparatorCMP12, that is, the steering force determination value V3 (refer to FIG.5) supplied from the leftward steering force discrimination leveldetermination unit 254 to the comparator CMP12 is determined by theresistors R14, R15 and R16.

When it is assumed that the resistance values of the resistors and thepower supply voltage of the power supply terminal are represented by thesame numerals as these components, the steering force determinationvalue V3 is represented by the following formula.

    V3={R15·R16/(R15+R16)}/[{R15·R16/(R15+R16)}+R14]×Vcc(3)

When the output from the comparator CMP11 is at the low level "L", themotor leftward drive is permitted. At the time, since the transistor TR3is turned off, the level of the inverting input terminal of thecomparator CMP12, that is, the steering force determination value V1(refer to FIG. 5) supplied from the leftward steering forcediscrimination level determination unit 254 to the comparator CMP12 isdetermined by the resistors R14, R15 and R16.

That is, the steering force determination value V1 is represented by thefollowing formula.

    V1=R15/(R14+R15)×Vcc                                 (4)

The operation of the motor drive direction restricting circuit 25 willbe described with reference to FIG. 5 in more detail.

In the drawing, LL shows the characteristics of the leftward steeringforce determination level and RL shows the characteristics of therightward steering force determination level. A motor drive permissionregion is located from LL to RL, the region above LL is a motor leftwarddrive prohibition region and the region below RL is a motor rightwarddrive prohibition region.

The relationship between the steering force determination values V1, V2,V3 and V4 as the steering force determination level is V2<V3<0<V4<V1,steering torque<0 means leftward steering, steering torque>0 meansrightward steering and steering torque=0 means neutral.

The leftward steering force determination level is determined by theleftward steering force discrimination level determination unit 254based on the output from the leftward torque comparison unit 252 andwhen the output from the leftward torque comparison unit 252 is in apermission state, the leftward steering force determination value is V1and when it is in a prohibition state, the leftward steering forcedetermination value is V3.

The rightward steering force determination level is determined by therightward steering force discrimination level determination unit 253based on the output from the rightward torque comparison unit 251 andwhen the output from the rightward torque comparison unit 251 is in thepermission state, the rightward steering force determination value is V2and when it is in the prohibition state, the rightward steering forcedetermination value is V4.

When a steering force is equal to or below the rightward steering forcedetermination value V2 or V4, the rightward torque comparison unit 251outputs a motor rightward drive prohibition signal to the AND circuits26a and 26b. On the contrary, when a steering force exceeds therightward steering force determination value V2 or V4, the rightwardtorque comparison unit 251 outputs a motor rightward drive permissionsignal to the AND circuits 26a and 26b.

This is also applicable to the operation of the leftward torquecomparison unit 252 and leftward steering force discrimination leveldetermination unit 254.

The electrically-driven power steering control apparatus assists andurges steering wheel operation and restricts the value sensed by thesteering torque sensor 1 equal to or below a predetermined level.

In FIG. 5, since the steering force determination values V1 and V2 areset larger than the predetermined level, when a steering torque, whichis generated when a motor output is in an abnormal state, exceeds thesteering force determination values V1 and V2, a motor drive directionis restricted.

In the motor drive direction restricting circuit 25, when, for example,a steering torque exceeds the leftward steering force determinationvalue V1 at a point a in rightward steering operation, the leftwardsteering force determination value V1 changes to V3. As a result, it isprohibited to drive the motor leftward so long as a steering torque ison the right side.

Further, when the motor is to be driven leftward, a steering torque mustbe generated on the left side and equal to or less than the leftwardsteering force determination value V3 (point b). At the time, theleftward steering force determination level returns from the leftwardsteering force determination value V3 to V1. That is, the leftwardsteering force determination level has such hysteresis characteristicsthat when a steering torque exceeds the leftward steering forcedetermination value V1, the determination level changes to V3, whereaswhen a steering torque is equal to or less than the leftward steeringforce determination value V3, it returns to V1.

This is also applicable to a rightward steering force determinationvalue in the same way and when a steering torque changes exceeding therightward steering force determination value V2 in leftward steeringoperation (point c), a rightward steering force determination levelchanges from the rightward steering force determination value V2 to V4.As a result, it is prohibited to drive the motor rightward so long asthe steering torque is on the left side.

Further, when the motor is to be driven rightward, a steering torquemust be generated on the right side and exceed the rightward steeringforce determination value V4 (point d). At the time, the rightwardsteering force determination level returns from the rightward steeringforce determination value V4 to V2. That is, when the steering torqueexceeds a steering force determination criterion, the motor is permittedto be driven only in the motor drive direction determined from thesteering torque. Consequently, even if an abnormal motor drive signal isoutput by the runaway of the CPU 22, the safety of the system is securedbecause the motor drive direction is restricted.

FIG. 4 is a circuit diagram showing an example of the specific circuitarrangement of the motor drive circuit 27.

In the drawing, the motor drive circuit 27 constitutes a bridge circuitby four field effect transistors (hereinafter, referred to as FET) 1-4.When, for example, only the FET 4 is fixed to an off state by the motordrive direction restricting circuit 25 in the state that a motor currentflows in the sequence of the FET 1, the motor 3 and the FET 4, the FET 1is turned on. Therefore, when the motor 3 is driven by steering wheeloperation, a regenerative current flows in the sequence of the motor 3,the parasitic diode of the FET 2 and the FET 1 so that a braking forceis applied to make the steering wheel operation heavy.

However, when the upper and lower stage FETs are turned off as shown inFIG. 4, the regenerative current does not flow and no braking force isapplied to the motor. That is, the FETs 1-4 can be turned off regardlessof the output levels of the I/F circuits 23 and 24 by turning off theoutput from the motor drive direction restricting circuit 25, wherebythe regenerative current does not flow so that no braking force isapplied to the motor.

With this arrangement, even if the motor is driven in an abnormal state,steering wheel operation can be carried out with a steering force nearto that in manual operation to thereby prevent the increase of adifference between a rightward steering wheel operating force and aleftward steering wheel operating force.

Further, since the motor drive direction restricting means restricts theoperation of a pair of the transistors of the bridge circuit, a brakingforce is prevented from being applied by a regenerative current flowingto the motor, so that the increase of the difference between therightward steering wheel operating force and the leftward steering wheeloperating force can be prevented when a motor drive direction isrestricted by the motor drive direction restricting means.

Embodiment 2

FIG. 6 is a circuit diagram showing the arrangement of an embodiment 2of the present invention. In the drawing, the same numerals as used inFIG. 1 are used to denote components corresponding to those in FIG. 1and the detailed description thereof is omitted.

A motor drive direction restricting circuit 25A in a controller 2Ainputs the signal from a steering torque sensor 1 to a rightward torquecomparison unit 251 and a leftward torque comparison unit 252. Therightward torque comparison unit 251 compares the rightward steeringforce determination level determined by a rightward steering forcediscrimination level determination unit 255 with the signal from thesteering torque sensor 1 and restricts the rightward drive of a motordepending upon the result of comparison. Further, the leftward torquecomparison unit 252 compares the leftward steering force determinationlevel determined by a leftward steering force discrimination leveldetermination unit 256 with the signal from the steering torque sensor 1and restricts the leftward drive of the motor depending upon the resultof comparison.

The rightward steering force determination level determined by therightward steering force discrimination level determination unit 255 isdetermined based on the result of the output from a motor rightwarddrive output I/F circuit 23. Further, the leftward steering forcedetermination level determined by the leftward steering forcediscrimination level determination unit 256 is determined based on theresult of the output from a motor leftward drive output I/F circuit 24.

Note, the rightward steering force determination level determined by therightward steering force discrimination level determination unit 255 maybe determined based on the signal output from a CPU 22 to the motorrightward drive output I/F circuit 23. Likewise, the leftward steeringforce determination level determined by the leftward steering forcediscrimination level determination unit 256 may be determined based onthe signal output from the CPU 22 to the motor leftward drive output I/Fcircuit 24.

Next, overall operation will be described.

When an output from the steering torque sensor 1 is supplied to the CPU22 through the torque signal input I/F circuit 21, the CPU 22 determinesa motor drive direction and a target motor current value based on thetorque signal from the torque signal input I/F circuit 21. When arightward torque is generated, the motor drive direction is a rightdirection and when a leftward torque is generated, the motor drivedirection is a left direction.

Further, the CPU 22 determines a motor output value from a differencebetween the motor current value sensed by the motor current sensingcircuit 28 and the target motor current value and outputs the motoroutput value to the motor rightward drive output I/F circuit 23 or motorleftward drive output I/F circuit 24.

When a motor rightward drive signal and the motor output value are inputto the motor rightward drive output I/F circuit 23 from the CPU 22, themotor rightward drive output I/F circuit 23 outputs a motor rightwarddrive output signal to the AND circuits 26a and 26b.

Likewise, when a motor leftward drive signal and the motor output valueare input to the motor leftward drive output I/F circuit 24 from the CPU22, the motor leftward drive output I/F circuit 24 outputs a motorleftward drive output signal to the AND circuits 26c and 26d.

The motor drive direction restricting circuit 25A restricts the motordrive direction based on the result of the output from the motorrightward drive output I/F circuit 23, the result of the output from themotor leftward drive output I/F circuit 24 and the output from thesteering torque sensor 1.

FIG. 7 a circuit diagram showing an example of the specific circuitarrangement of the motor drive direction restricting circuit 25A. Note,in the drawing, the same numerals as used in FIG. 3 are used to denotecomponents corresponding to those in FIG. 3 and the detailed descriptionthereof is omitted.

In the drawing, the comparator CMP11 constituting the rightward torquecomparison unit 251 has a non-inverting input terminal connected to thenode where voltage dividing resistors R11 and R12, which are connectedbetween a power supply terminal Vcc and the ground, are connected.Further, the collector of a transistor TR4 is connected through aresistor R17 to the node where the voltage dividing resistors R11 andR12 are connected, the output of the motor rightward drive output I/Fcircuit 23 is supplied to the base of the transistor TR4 and the emitterthereof is grounded. The inverting input terminal of the comparatorCMP11 is supplied with the steering torque from the steering torquesensor 1.

The components other than the comparator CMP11 constitute the rightwardsteering force discrimination level determination unit 255.

Likewise, the comparator CMP12 constituting the leftward torquecomparison unit 252 has an inverting input terminal connected to thenode where voltage dividing resistors R14 and R15, which are connectedbetween the power supply terminal Vcc and the ground, are connected.

The non-inverting input terminal of the comparator CMP12 is suppliedwith the steering torque from the steering torque sensor 1.

Further, the collector of a transistor TR5 is connected through aresistor R18 to the node where the voltage dividing resistors R14 andR15 are connected, the emitter of the transistor TR5 is connected to thepower supply terminal Vcc and the base thereof is connected to thecollector of a transistor TR6 at a previous stage through a resistor.The output of the motor leftward drive output I/F circuit 24 is suppliedto the base of the transistor TR6 and its emitter is grounded. Thecomponents other than the comparator CMP 12 constitute the leftwardsteering force discrimination level determination unit 256.

The comparator CMP11 compares the level of the non-inverting inputterminal with the level of the inverting input terminal. That is, thecomparator CMP11 compares the output from the rightward steering forcediscrimination level determination unit 255 with the level of outputfrom the steering torque sensor 1 and when the level of thenon-inverting input terminal is larger than the level of the invertinginput terminal, the comparator CMP11 outputs the high level "H", whereaswhen the level of the non-inverting input terminal is smaller than thelevel of the inverting input terminal, it outputs the low level "L".

When the output from the comparator CMP11 is at the high level "H",motor rightward drive is prohibited. Further, since the transistor TR4is turned on when the output from the motor rightward drive output I/Fcircuit 23 is at the high level "H", the level of the non-invertinginput terminal of the comparator CMP11, that is, the steering forcedetermination value V4 (refer to FIG. 8) supplied from the rightwardsteering force discrimination level determination unit 255 to thecomparator CMP11 is determined by the resistors R11, R12 and R17.

When the output from the comparator CMP11 is at the low level "L", motorrightward drive is permitted. Further, since the transistor TR4 isturned off when the output from the motor rightward drive output I/Fcircuit 23 is at the low level "L", the level of the non-inverting inputterminal of the comparator CMP11, that is, the steering forcedetermination value V2 (refer to FIG. 8) supplied from the rightwardsteering force discrimination level determination unit 255 to thecomparator CMP11 is determined by the resistors R11, R12.

The comparator CMP12 compares the level of the inverting input terminalwith the level of the non-inverting input terminal. That is, thecomparator CMP12 compares the output from the leftward steering forcediscrimination level determination unit 256 with the level of the outputfrom the steering torque sensor 1 and when the level of the invertinginput terminal is larger than the level of the non-inverting inputterminal, the comparator CMP12 outputs the low level "L", whereas whenthe level of the inverting input terminal is smaller than the level ofthe non-inverting input terminal, the comparator CMP12 outputs the highlevel "H".

When the output from the comparator CMP12 is at the high level "H",motor leftward drive is prohibited. Further, since the transistors TR6and TR5 are turned on together when the output from the motor leftwarddrive output I/F circuit 24 is at the high level "H", the level of theinverting input terminal of the comparator CMP12, that is, the steeringforce determination value V3 (refer to FIG. 8) supplied from theleftward steering force discrimination level determination unit 256 tothe comparator CMP12 is determined by the resistors R14, R15 and R18.

When the output from the comparator CMP12 is at the low level "L", themotor leftward drive is permitted. Further, since the transistors TR6and TR5 are turned off together when the output from the motor leftwarddrive output I/F circuit 24 is at the low level "L", the level of theinverting input terminal of the comparator CMP12, that is, the steeringforce determination value V1 (refer to FIG. 8) supplied from theleftward steering force discrimination level determination unit 256 tothe comparator CMP12 is determined by the resistors R14, R15.

The operation of the motor drive direction restricting circuit 25A willbe described with reference to FIG. 8 in more detail.

In the drawing, LL shows the characteristics of the leftward steeringforce determination level and RL shows the characteristics of therightward steering force determination level. A motor drive permissionregion ranges from LL to RL, the region above LL is a motor left driveprohibition region and the region below RL is a motor right driveprohibition region.

The relationship between the steering force determination values V1, V2,V3 and V4 as the steering force determination level is V2<V3<0<V4<V1,steering torque<0 means leftward steering, steering torque>0 meansrightward steering and steering torque=0 means neutral.

RD shows the output from the motor rightward drive output I/F circuit 23(motor rightward drive signal) and LD shows the output from the motorleftward drive output I/F circuit 24 (motor leftward drive signal) andthey represent motor drive stop (OFF) at the high level "H" and motordrive (ON) at the low level.

For example, when a leftward steering torque is sensed and the motorleftward drive signal LD is turned on (point e), the leftward steeringforce determination value V1 changes to V3. As a result, when a steeringtorque changes exceeding the leftward steering force determination valueV3 in the state that the motor leftward drive signal LD output from themotor leftward drive output I/F circuit 24 is turned on, the leftwardtorque comparison unit 252 outputs a motor leftward drive prohibitionsignal to one of the input terminals of each of the AND circuits 26c,26d, respectively.

When the input signal coincides with the output from the motor leftwarddrive output I/F circuit 24 which is supplied to the other inputterminal of each of the AND circuits 26c, 26d, that is, a motor leftwarddrive signal, the AND circuit 26c, 26d drive the motor 3 leftward by themotor drive circuit 27.

Further, when the motor leftward drive signal LD output from the motorleftward drive output I/F circuit 24 is turned off (point f), thesteering force determination level returns from the leftward steeringforce determination value V3 to V1 to release the motor leftward driverestriction. This is also applied likewise when the motor rightwarddrive signal RD output from the motor rightward drive output I/F circuit23 is turned on (point g) and when the motor rightward drive signal RDis turned on (point g), the rightward steering force determination levelV2 changes to V4. As a result, when a steering torque changes equal toor less than V4 in the state that the motor rightward drive signal RD isturned of, the rightward torque comparison unit 251 outputs a motorrightward drive prohibition signal to one of the input terminals of eachof the AND circuits 26a, 26b.

When the input prohibition signal coincides with the output from themotor rightward drive output I/F circuit 23 which is supplied to theother input terminal of each of the AND circuits 26a, 26b, that is, amotor rightward drive signal, the AND circuits 26a, 26b drive the motor3 rightward by the motor drive circuit 27.

Further, when the motor rightward drive signal RD is turned off (pointh), the steering force determination level returns from V4 to V2 torelease the motor rightward drive restriction.

With this operation, a motor drive region corresponding to a motor drivestate can be set and when a steering torque outside the motor driveregion is sensed, a motor drive direction is restricted. Thus, safety issecured and reliability is improved. Further, when the a motor driverestricting direction is released, since a motor output is stopped, evenif the restriction made by motor drive direction restricting means isreleased, the motor is not driven and safety is secured.

This method has a feature that the direction in which the motor can bedriven is fixed by the motor drive signals RD and LD.

Further, when the state of the motor drive signal (RD, LD) is switchedin FIG. 8, the steering force determination level changes beyond aneutral level. That is, when the motor drive means changes to a motordrive state or the motor drive direction restricting circuit changes toa motor drive direction restricting state, the steering forcedetermination level changes beyond the neutral level of a steeringforce.

With this operation, when a steering wheel is released in the state thata motor dive direction is fixed leftward due to, for example, anabnormal motor output from the CPU 22, a steering torque is madeneutral. Since a steering force determination value is has a valuebeyond neutral (V3), motor leftward drive is prohibited in the neutralsteering torque. That is, even if a motor output is made abnormal whenthe steering wheel is released, inconvenience such as the self-turn ofthe steering wheel and the like is not caused.

In FIG. 8, when the motor is not driven, the steering forcedetermination level is set by the steering force determination values V1and V2. That is, the steering force determination level is set to alevel for releasing the restriction made by the motor drive directionrestricting circuit.

With this arrangement, when the motor drive direction is restricted inthe state that the motor is not driven (motor output is stopped becausea steering torque is neutral), even if the motor is driven in therestricted direction, steering operation may be not assisted by themotor because the motor drive direction is restricted (steering wheeloperation is made heavy). For example, when the steering forcedetermination value is set to V3 or V4 in the state that the motor isnot driven, a motor drive prohibition region is set between V3 and V4(same as a neutral prohibition method) and the motor may be difficult tobe smoothly driven. However, since the steering force determinationlevel is set by the steering force determination values V1 and V2 asdescribed above when the motor is not driven, such a problem is notcaused.

In FIG. 8, when the motor is not driven, V1 and V2 are set as thesteering force determination values. That is, when the restriction ofthe motor drive direction is released by the motor drive directionrestricting circuit, the steering force determination level is setlarger than a predetermined value. With this arrangement, when a motorcurrent control is effected to feed a braking current to slow the turnspeed of the steering wheel, a direction in which a steering torque isgenerated is opposite to a motor drive direction. However, since thesteering force determination value V1 or V2 is set larger than a torquegenerated at the time, a motor output is permitted and redundancy isprovided with the motor current control. For example, V1 is set to avalue exceeding a rightward steering torque of 30 kgfcm and V2 is set toa value exceeding a leftward steering torque of 30 kgfcm.

As described above, according to this embodiment, since the steeringforce determination level changes with a predetermined delay elementwith respect to the change of state of the motor drive means as well asis kept to a predetermined level corresponding to the state of the motordrive means, the restriction of the motor drive direction is notreleased until motor drive is set to a stop state. Consequently, safetyis improved because a motor output is not permitted unless the polarityof a motor drive direction coincides with the polarity of a steeringtorque.

Since the steering force determination level changes beyond the neutrallevel of a steering force when the motor drive means changes to a motordrive state or the motor drive direction restricting means changes to amotor drive direction restricting state, the self-turn of the steeringwheel is prevented when it is released from a hand in an abnormal motoroutput.

When the motor is not driven, since the steering force determinationlevel is set to the level at the time when the restriction made by themotor drive direction restricting means is released, a sufficientassisting force can be obtained from the balance with the delay ofchange of the steering force determination level when the motor is driveand steering feel is improved.

Further, since the steering force determination level is set larger thanthe predetermined value when the restriction of the motor drivedirection made by the motor drive direction restricting means isreleased, a motor drive neutral permission region can be set wide aswell as when the steering force determination level is set by H/W, aresistor and the like do not require accuracy. In addition, since theneutral permission region can be set wide, an assisting force neededwhen the steering wheel starts to be cut, a braking force forsuppressing the turn speed of the steering wheel and the like can becontrolled.

Embodiment 3

FIG. 9 is a circuit diagram showing the arrangement of an embodiment 3of the present invention. In the drawing, the same numerals as used inFIG. 1 are used to denote components corresponding to those in FIG. 1and the detailed description thereof is omitted.

A motor drive direction restricting circuit 25B in a controller 2Binputs the signal from a steering torque sensor 1 to a rightward torquecomparison unit 251 and a leftward torque comparison unit 252. Therightward torque comparison unit 251 compares the rightward steeringforce determination level determined by a rightward steering forcediscrimination level determination unit 257 with the signal from thesteering torque sensor 1 and restricts the rightward drive of a motorbased on the result of comparison.

Further, the leftward torque comparison unit 252 compares the leftwardsteering force determination level determined by a leftward steeringforce discrimination level determination unit 258 with the signal fromthe steering torque sensor 1 and restricts the leftward drive of themotor based on the result of comparison.

The rightward steering force determination level determined by therightward steering force discrimination level determination unit 257 isdetermined based on the result of the output from the rightward torquecomparison unit 251 and output from a motor rightward drive output I/Fcircuit 23. Further, the leftward steering force determination leveldetermined by the leftward steering force discrimination leveldetermination unit 258 is determined based on the result of the outputfrom the leftward torque comparison unit 252 and the output from a motorleftward drive output I/F circuit 24.

Note, although an example of the specific arrangement of the motor drivedirection restricting circuit 25B is not shown, it may be composed ofthe circuit in FIG. 3 and the circuit in FIG. 7 in combination.

Further, the rightward steering force determination value determined bythe rightward steering force discrimination level determination unit 257may be determined based on the signals output from the rightward torquecomparison unit 251 and a CPU 22 to the motor rightward drive output I/Fcircuit 23. Likewise, the leftward steering force determination valuedetermined by the leftward steering force discrimination leveldetermination unit 258 may be determined based on the signals outputfrom the leftward torque comparison unit 252 and the CPU 22 to the motorleftward drive output I/F circuit 24.

Next, operation will be described.

Note, since overall operation is substantially the same as those of FIG.1 and FIG. 6, the description thereof is omitted and only the portionsdifferent from the aforesaid, that is, the operation of the motor drivedirection restricting circuit 25B will be described with reference toFIG. 10.

In the drawing, LL shows the characteristics of the leftward steeringforce determination level and RL shows the characteristics of therightward steering force determination level. A motor drive permissionregion ranges from LL to RL, the region above LL is a motor left driveprohibition region and the region below RL is a motor right driveprohibition region. The relationship between the steering forcedetermination values V1, V2, V3 and V4 is V2<V3<0<V4<V1, steeringtorque<0 means leftward steering, steering torque>0 means rightwardsteering and steering torque=0 means neutral.

RD shows the output from the motor rightward drive output I/F circuit 23(motor rightward drive signal) and LD shows the output from the motorleftward drive output I/F circuit 24 (motor leftward drive signal) andthey represent motor drive stop (OFF) at the high level "H" and motordrive (ON) at the low level.

For example, when a leftward steering torque is sensed and the motorleftward driving signal LD is turned on (point i), the leftward steeringforce determination value V1 changes to V3. As a result, when a steeringtorque changes exceeding the leftward steering force determination valueV3 in the state that the motor leftward drive signal LD output from themotor leftward drive output I/F circuit 24 is turned on, the leftwardtorque comparison unit 252 outputs a motor leftward drive prohibitionsignal to one of the input terminals of each of AND circuits 26c, 26d,respectively.

When the input prohibition signal coincides with the output from themotor leftward drive output I/F circuit 24 which is supplied to theother input terminal of each of the AND circuits 26c, 26d, that is, amotor leftward drive signal, the AND circuits 26c, 26d drive the motor 3leftward by the motor drive circuit 27.

Further, when the motor leftward drive signal LD output from the motorleftward drive output I/F circuit 24 is turned off (point i), thesteering force determination level returns from V3 to V1 unless a motorleftward drive direction is not restricted by the leftward torquecomparison unit 252. This is also applied likewise when the motorrightward drive signal RD output from the motor rightward drive outputI/F circuit 23 is turned on (point k) and when the motor rightward drivesignal RD is turned on (point k), the rightward steering forcedetermination level V2 changes to V4. As a result, when a steeringtorque changes equal to or less than V4 in the state that the motorrightward drive signal RD is turned on, the rightward torque comparisonunit 251 outputs a motor rightward drive prohibition signal to one ofthe input terminals of each of AND circuits 26a and 26b.

When the input prohibition signal coincides with the output from themotor rightward drive output I/F circuit 23 which is supplied to theother input terminal of each of the AND circuits 26a, 26b, that is, amotor rightward drive signal, the AND circuits 26a, 26b drive the motor3 rightward by a motor drive circuit 27.

Further, when the motor rightward drive signal RD is turned off (pointl), the steering force determination level does not return from V4 to V2unless the restriction against a motor drive direction made by therightward torque comparison unit 251 is not released and it returns fromV4 to V2 after the restriction of the motor drive direction made by therightward torque comparison unit 251 is released.

As described above, since this embodiment enables a motor drive regioncorresponding to a motor drive state to be set and restricts a motordrive direction when a steering torque outside the motor drive region issensed, safety is secured and reliability is improved. Further, even ifthe motor is stopped, the steering force determination level does notreturn to its original value unless the motor drive direction isrestricted by the motor drive direction restricting circuit and thus themotor drive direction is kept in the restricted state. With thisoperation, since the motor is securely restricted, the safety of thesystem can be improved.

That is, a motor drive prohibition region can be set corresponding to amotor drive state, safety is secured and reliability is improved. Sincea motor output is stopped when a motor drive restricting direction beingkept is released, the motor is not driven when the restriction made bythe motor drive direction restricting means is released. Further, sincethe motor output prohibition region is fixed until a motor drive stateand steering torque return to their normal states, the safety of thesystem can be improved.

Embodiment 4

FIG. 11 is a circuit diagram showing the arrangement of the main portionof an embodiment 4 of the present invention.

Since the overall circuit of this embodiment is similar to that shown inFIG. 6, FIG. 11 shows only an example of the specific circuitarrangement of a motor drive direction restricting circuit 25A which isa circuit arrangement characteristic to this embodiment. Note, in thedrawing, the same numerals as used in FIG. 7 are used to denotecomponents corresponding to those in FIG. 7 and the detailed descriptionthereof is omitted.

This embodiment is arranged such that a delay is provided with thechange of a steering force determination level so that when a steeringwheel is turned while released from a hand, a motor is controlled torestrict the turn of the steering wheel.

To achieve the above control, a capacitor C1 is connected in parallelwith a resistor R12 as one of dividing resistors connected between thenon-inverting input terminal of a comparator CMP11 constituting arightward torque comparison unit 251 and the ground, that is, between apower supply terminal Vcc and the ground.

The components other than the comparator CMP11 constitute a rightwardsteering force discrimination level determination unit 255.

Likewise, a capacitor C2 is connected in parallel with a resistor R14 asone of dividing resistors connected between the inverting input terminalof a comparator CMP12 constituting a leftward torque comparison unit 252and the ground, that is, between the power supply terminal Vcc and theground.

The components other than the comparator CMP12 constitutes a leftwardsteering force discrimination level determination unit 256.

Since a transistor TR4 is turned on when the output from a motorrightward drive output I/F circuit 23 is at the high level "H", thelevel of the non-inverting input terminal of the comparator CMP11, thatis, the steering force determination value V2 supplied from therightward steering force discrimination level determination unit 255 tothe comparator CMP11 is determined by the resistors R11, R12 and R17.

When it is assumed that the resistance values of the resistors and thepower supply voltage of the power supply terminal are represented by thesame numerals as those of these components, the steering forcedetermination value V2 is represented by the following formula.

    V2={R12·R17/(R12+R17)}/[{R12·R17/(R12+R17)}+R11]×Vcc(5)

Since the transistor TR4 is turned off when the output from the motorrightward drive output I/F circuit 23 is at the low level "L", the levelof the non-inverting input terminal of the comparator CMP11, that is,the steering force determination value V4 supplied from the rightwardsteering force discrimination level determination unit 255 to thecomparator CMP11 is determined by the resistors R11 and R12. That is,the steering force determination value V4 is represented by thefollowing formula.

    V4=R12/(R11+R12)×Vcc                                 6)

where, V4>V2.

When it is assumed that the time constant (discharge) of the capacitorC1 is T₁ when the transistor TR4 is turned on and the time constant(charge) thereof is T₂ when the transistor TR4 is turned off, thecharge/discharge time constant of the capacitor C1 is determined by thefollowing formula.

    T.sub.1 =C1×R11R12∥R17                      (7)

    T.sub.2 =C1×R11∥R12                         (8)

where, C1 is the capacitance value of the capacitor C1 and ∥ shows thatthe respective resistors are connected in parallel with each other inthe above formulas.

Next, operation will be described with reference to FIG. 12 and FIG. 13.

FIG. 12 explains the operation executed when the time constant of thesteering force determination level which changes when motor drivesignals RD, LD are turned on is delayed with respect to the timeconstant of the steering force determination level which changes whenthe motor drive signals RD, LD are turned off.

FIG. 12 shows the characteristics of steering force determination levelsLL and RL when the motor drive signals RD and LD are alternately output.

The time constant of the change of the characteristics LL and RL of thesteering force determination level is different depending upon whetherthe motor drive signals RD, LD are turned on or off. Therefore, in thecase of the characteristics LL of the leftward steering forcedetermination level, for example, the leftward steering forcedetermination value only changes up to a certain value between 0 and V1and further changes depending upon the frequency of the motor drivesignal LD. That is, when the frequency is higher, the leftward steeringforce determination value has a value near to V1. More specifically,when steering operation is repeated at a high speed, a motor drivepermission range (between LL and RL) is widened in accordance with asteering frequency. With this arrangement, the malfunction of the motordrive direction restricting circuit 25A can be prevented and further thedelay of phase of a motor current and a steering torque can be correctedwithout being disturbed by the motor drive direction restricting circuit25A. As a result, it can be said that the motor can be controlled withredundancy.

FIG. 13 explains why the steering force determination level must bedelayed when the motor drive signals LL, RL are turned on.

For example, when the steering wheel turns while being released from ahand, the motor may be driven to restrict the turn of the steeringwheel. In such as case, a steering torque is generated in an oppositedirection to a motor drive direction when the motor is driven. In FIG.13, the motor is driven rightward (RD=L) at a point n and at the time asteering torque t is generated in the left direction and then returns tothe right direction. The leftward steering torque is caused by theinertia of the steering wheel and the like. Further, as apparent fromFIG. 13, if the delay is not provided with the steering forcedetermination level, when the steering wheel turns while released from ahand, the motor cannot be controlled to restrict the turn of thesteering wheel. That is, redundancy is lost when the motor iscontrolled.

As described above, according to this embodiment, since the steeringforce determination level changes with a predetermined delay elementwith respect to the change of state of the motor drive means as well assince the speed change of the steering force determination level causedwhen the motor drive means changes from a stop state to a drive state isdelayed with respect to the speed change caused when the motor drivemeans changes from the drive state to the stop state, when the motor isrepeatedly driven and stopped, the steering force determination level isprevented from being lowered. Further, the steering force determinationlevel is provided with the delay when the motor drive means changes fromthe stop state to the drive state, the motor can be driven in adirection where the polarity of a steering torque is different from thepolarity of a motor drive direction for a predetermined period of time.As a result, the motor control is provided with redundancy.

Embodiment 5

FIG. 14 is a view explaining an embodiment 5 of the present invention.

Since the overall circuit of this embodiment is similar to that of FIG.6 and a motor drive direction restricting circuit 25A which is a circuitarrangement characteristic to this embodiment is also similar to that ofFIG. 11, they are not described here.

FIG. 14 explains the operation when the time constant of a steeringforce determination level which changes depending upon the output signalfrom a rightward torque comparison unit 251 or a leftward torquecomparison unit 252 is set faster than the time constant of the steeringforce determination level which changes when motor drive signals RD, LDare turned on.

FIG. 14 shows a waveform when a steering torque exceeds a leftwardsteering force determination value while a leftward drive signal LD isturned on at a point o and the leftward steering force determinationvalue changes. The steering torque exceeds the leftward steering forcedetermination value at a point p and the time constant of the steeringforce determination level changes. Since the steering forcedetermination level instantly changes when the steering torque exceedsthe steering force determination value in FIG. 14, when an abnormaltorque is generated by an abnormal motor output and the like, a motordrive direction is instantly restricted and the safety of the system canbe increased.

As described above, according to this embodiment, since the steeringforce determination level changes with a predetermined delay elementwith respect to the change of state of motor drive means or the changeof state of the motor drive direction restricting means as well as thechange speed of the steering force determination level caused by thechange of state of the motor drive direction restricting means is setfaster than the change speed of the steering force determination levelcaused by the change of state of the motor drive means, when an abnormalsteering force is generated by the occurrence of an abnormal motoroutput and the like . The steering force determination levvel instantlychanges to restrict a direction in which the motor can be driven.

Embodiment 6

FIG. 15 is a circuit diagram showing the arrangement of an embodiment 6of the present invention. In the drawing, the same numerals as used inFIG. 9 are used to denote components corresponding to those in FIG. 9and the detailed description thereof is omitted.

In the drawing, a phase compensation circuit 29 is disposed in front ofa torque signal input I/F circuit 21 and it subjects the signal from asteering torque sensor 1 to phase compensation and outputs thephase-compensated value to a motor drive direction restricting circuit25B and a CPU 22 through a torque signal input I/F circuit 21.

The motor drive direction restricting circuit 25B inputs thephase-compensated steering torque signal to a rightward torquecomparison unit 251 and a leftward torque comparison unit 252.

Next, operation will be described.

Note, although the detailed description of overall operation is omittedbecause it is substantially similar to the cases of FIG. 1 and FIG. 6,the operation will be briefly described using FIG. 16 which shows thephase compensation circuit 29 and the CPU 22 and the like whose internalarrangement is similar to that of FIG. 2. Note, to simplify thedescription, I/F circuits 21, 23, 24, a motor drive circuit 27, a motorcurrent sensing circuit 28 and the like are omitted in FIG. 16.

The steering torque sensed by the steering torque sensor 1 is subjectedto phase compensation by phase compensation means 221 in the CPU 22 andtarget current determination means 222 determines a target current usingthe phase-compensated torque value. A current flowing to a motor 3 issensed by a motor current sensing means 223. Then, a difference betweenthe target current value determined by the target current determinationmeans 222 and the motor current sensed by the motor current sensingmeans 223 is determined and motor drive means 224 outputs a motor drivesignal based on the difference. The motor drive signal serves as themotor drive signal of the CPU 22.

The steering torque sensed by the steering torque sensor 1 is input tothe phase compensation circuit 29 and the motor drive directionrestricting circuit 25B outputs a motor drive direction restrictingsignal using the signal having a phase compensated by the phasecompensation circuit 29. Then, the motor 3 is driven in response to thesignal obtained by ANDing the motor drive signal from the CPU 22 and themotor drive signal from the motor drive direction restricting circuit25B through an AND circuit 26. Malfunction caused by the motor drivedirection restricting circuit 25B due to the dislocation of a phase isprevented by adjusting the coefficients of the phase compensation means221 in the CPU 22 and phase compensation circuit 29.

As described above, according to this embodiment, since the phasecompensation means is interposed between the steering force sensingmeans and the motor drive direction restricting means, the hunting of amotor current caused by the difference between the response speed of thecontrol system and the response speed of the motor drive directionrestricting means can be suppressed.

Embodiment 7

FIG. 17 is a view explaining an embodiment 7 of the present inventionand shows the relationship between a vehicle speed and a steeringtorque.

In this embodiment, when a motor drive direction restricted by theaforesaid motor drive direction restricting circuit is released, asteering force determination level is set with respect to a vehiclespeed.

With this arrangement, a steering torque generated when the vehiclespeed exceeds Ve1 is restricted by a self-alignment torque, the frictionforce of a road surface, the steering angle of a steering wheel and thelike, as apparent from FIG. 17. That is, when a steering torqueexceeding Vx is generated at the vehicle speed exceeding Ve1, it isdetermined that a motor output is abnormal. The reliability and safetyof the system are improved by setting the torque Vx as the steeringforce determination level.

As described above, according to this embodiment, since the steeringforce determination level is set with respect to the vehicle speed whenthe motor drive direction restricted by the aforesaid motor drivedirection restricting circuit is released, such operation can beprevented, for example, that a rightward steering force which isgenerated by a steering wheel cut rightward while travelling at a highspeed exceeds a leftward steering force determination level andrestricts a motor leftward drive direction. Further, this is alsoapplicable when the steering wheel is cut leftward in the same way.

Embodiment 8

FIG. 18 is a view explaining an embodiment 8 of the present invention.In the drawing, the same numerals as used in FIG. 15 are used to denotecomponents corresponding to those in FIG. 15 and the detaileddescription thereof is omitted.

In the drawing, a clutch 4 for coupling a motor 3 with a steering systemcan be engaged and disengaged in response to the clutch drive signalfrom a controller 2D.

A clutch drive circuit 30 turns on and off the clutch 4 in response tothe clutch drive signal from the CPU 22 and switches 31a and 31bdisposed in the controller 2D are opened and closed in response to theclutch drive signal from the CPU 22.

The switch 31a is connected to the output of a rightward torquecomparison unit 251 from which a rightward drive restricting signal isoutput and the switch 31b is connected to the output of a leftwardtorque comparison unit 252 from which a leftward drive restrictingsignal is output.

Next, operation will be briefly described with reference to FIG. 19.

First, whether a clutch drive signal is output or not is determined,that is, whether the clutch 4 is engaged or not (step S1) and when theclutch drive signal is output, the process is ended.

Further, when the clutch drive signal is not output, whether the lock ofthe motor 3 is checked or not is determined (step S2). When the lock ofthe motor 3 is checked, the process is ended, whereas when the lock ofthe motor 3 is not checked, it is checked (step S3).

When the clutch 4 is disengaged, the output from the a motor drivedirection restricting circuit 25B can be made invalid by opening theswitches 31a and 31b.

With this arrangement, it is possible to drive the motor 3 when theclutch 4 is disengaged and sense the abnormal state of the motor 3 fromthe drive state of the motor 3.

Note, the switches 31a and 31b may be composed to transistors or thelike.

As described above, according to this embodiment, since the restrictionmade by motor drive direction restricting means is released when theclutch is disengaged, an abnormal state such as motor lock and the likecan be checked by freely driving the motor in a safe state.

Embodiment 9

FIG. 20 is a functional block diagram showing a embodiment 9 of thepresent invention. In the drawing, the same numerals as used in FIG. 2are used to denote components corresponding to those in FIG. 2 and thedetailed description thereof is omitted.

In this embodiment, motor drive direction restricting means issubstantially incorporated in a CPU 22A. An AND circuit 26 and the likeare not shown in the drawing.

The CPU 22A is composed of phase compensation means 221 for compensatingthe phase of the steering torque sensed by a steering torque sensor 1,target current determination means 222 for determining a current to beflown to a motor 3 from the phase-compensated signal, motor currentsensing means 223 for sensing a current flowing to the motor 3, motordrive direction restricting means 225 for estimating its operation fromthe steering torque and outputting a motor drive direction restrictingsignal and motor drive means 224 for determining a motor output valuefrom a difference between the target current determined by the targetcurrent determination means 222 and the motor current sensed by themotor current sensing means 223 and driving the motor 3 in accordancewith the motor output value.

As an overall circuit the circuit shown in FIG. 1 from which the motordrive direction restricting circuit 25 is removed may be used as anexample.

It is found from the functional block diagram that a motor current isfed back in the control system. In this feedback control system, whenthe feed of a motor current is prohibited at a portion which is notrelated to a motor current control loop, a target current other thanzero is instructed, whereas when the motor current is zero, it iscontemplated that the motor current is abnormally fed back. However, theoccurrence of abnormal feed back is prevented by providing the motordrive direction restricting means 225 and setting the motor targetcurrent to zero when a motor output is prohibited.

Next, operation will be described with reference to the flowchart ofFIG. 21.

The steering torque sensed by the steering torque sensor 1 is input tothe phase compensation means 221 through a torque signal input I/Fcircuit 21 for phase compensation and then it is input to the targetcurrent determination means 222 (step S21) to thereby determine a targetcurrent from the steering torque (step S22). Then, a motor drivedirection is also determined from the steering torque (step S23). Next,a motor current is input to the motor current sensing means 223 througha motor current sensing circuit 28 (step S24).

A motor drive restricting direction is determined from the steeringtorque by the motor drive direction restricting means 225 (step S25).

Next, the target current determination means 222 compares the motordrive direction determined by the target current determination means 222at step S23 with the motor drive restricting direction determined atstep S25 (step S26). When they coincide with each other, a coincidenceflag is set (step S27) and the target current is set to zero (step S28).Whereas, when they do not coincide with each other, the coincidence flagis cleared (step S29).

Then, a deviation between the target current and the sensed current isdetermined (step S30) and the motor drive means 224 determines a motoroutput value from the deviation (step S31). Next, the state of thecoincidence flag operated at step S27 or step 29 is checked (step S32)and when the flag is set, the motor output value is set to zero (stepS33) and a motor output is executed (step S34).

With this operation, a motor drive direction is substantially restrictedby the motor drive direction restricting means 225 and even if a motorcurrent is not normally fed back, an abnormal state is not caused to themotor current control system.

As described above, according to this embodiment, when a motor drivedirection is restricted by the motor drive direction restricting means,since the motor output is stopped and the target motor current is set tozero, the occurrence of an abnormal state of the feedback system(abnormal feedback of the motor current) is prevented.

Embodiment 10

FIG. 22 is a block diagram showing the arrangement of an embodiment 10of the present invention. In the drawing, the same numerals as used inFIG. 1 are used to denote components corresponding to those in FIG. 1and the detailed description thereof is omitted.

In this embodiment, the rightward steering force determination valuedetermined by a rightward steering force discrimination leveldetermination unit 253 and the leftward steering force determinationvalue determined by a leftward steering force discrimination leveldetermination unit 254 are input to a CPU 22B, these units 253 and 254being disposed in a motor drive direction restricting circuit 25 of acontroller 2E. The other arrangement of the embodiment 10 is similar tothat of FIG. 1.

Next, operation will be described with reference to the flowchart ofFIG. 23. Note, the same numerals as used in FIG. 21 are used to denotesteps similar to those of FIG. 21 for description.

The steering torque sensed by the steering torque sensor 1 is inputthrough a torque signal input I/F circuit 21 (step S21) to determine atarget current from the steering torque (step S22). A motor drivedirection is also determined from the steering torque (step S23). Next,a motor current is input through a motor current sensing circuit 28(step S24).

Next, the rightward steering force determination value determined by therightward steering force discrimination level determination unit 253 isinput (step S35) and further the leftward steering force determinationvalue determined by the leftward steering force discrimination leveldetermination unit 254 is input (step S36).

Then, the motor drive direction determined at step S23 is compared withthe steering force determination values input at step S35 and S36 todetermine whether the levels of the respective steering forcedetermination values are normal or not (step S37). When they are normal,a deviation between the target current and the sensed current isdetermined (step S30) and a motor output value is determined from thedeviation (step S31). Then, a motor output is executed (step S34).

On the other hand, when the levels of the respective steering forcedetermination values are not normal at step S37, the abnormal state ofthem is fixed (step S38) and a motor 3 is set to a non-driving state(step S39). Note, in the aforesaid, the steering force determinationvalues are preset within the range to which a steering torque can beinput. Further, when the abnormal state is fixed at step S38, apredetermined wait time may be provided.

With this operation, the CPU 22B can monitor the steering forcedetermination values and the abnormal state of the motor drive directionrestricting circuit 25 and the like can be sensed.

As described above, according to this embodiment, since the steeringforce determination levels are set within the range to which an inputcan be executed by steering force means, the abnormal state of thesteering force determination levels can be checked.

Embodiment 11

FIG. 24 is a block diagram showing the arrangement of an embodiment 11of the present invention. In the drawing, the same numerals as used inFIG. 1 are used to denote components corresponding to those in FIG. 1and the detailed description thereof is omitted.

In this embodiment, the rightward drive restricting signal from arightward torque comparison unit 251 and the leftward drive restrictingsignal from a leftward torque comparison unit 252 are input to a CPU22C, these units 251, 252 being disposed in a motor drive directionrestricting circuit 25 in a controller 2F, so that the CPU 22C canmonitor a motor drive restricting direction. The other arrangement ofthe embodiment 11 is similar to that of FIG. 1.

Next, operation will be described with reference to the flowchart ofFIG. 25.

Whether or not the steering torque sensed by a steering torque sensor 1is, for example, 40 kgfcm or less (step S41) is determined (step S41)and when it is 40 kgfcm or less, whether or not a motor drive directioncoincides with the motor drive direction restricted by the motor drivedirection restricting circuit 25 is determined at step S42. When theyare coincide with each other, an elapsed time is measured by a timer(not shown) at step S43 and whether 500 ms, for example, elapsed or notis determined, and when 500 ms elapsed, an abnormal state occurrenceflag is set (step S45) and a motor output is stopped (step S47).

When the steering torque exceeds 40 kgfcm at step S41, or when it isdetermined at step S42 that the motor drive directions do not coincidewith each other, whether the abnormal state occurrence flag is set ornot is determined at step S44, and when it is set, the motor output isstopped at step S47. Further, when the flag is not set, the 500 ms timeris cleared at step S46 and then the motor output is executed at stepS48. Further, the motor output is executed at step S48 until 500 mselapses at step S43.

With this operation, the abnormal state of the motor output and the likeof the motor drive direction restricting circuit 25 and the CPU 22C canbe sensed.

As described above, according to this embodiment, since motor drive isprohibited when a steering force is equal to or less than apredetermined value and a motor drive direction is restricted longerthan a predetermined time by the motor drive direction restrictingmeans, the abnormal state of the motor drive direction restricting meansand motor output system can be sensed and a motor output is prohibitedwhen an abnormal state occurs, thus safety is improved.

Embodiment 12

FIG. 26 is a flowchart showing an embodiment 21 of the presentinvention.

The circuit of this embodiment is arranged, for example, as shown by thecircuit of FIG. 24.

Next, operation will be described with reference to the flowchart ofFIG. 26. Note, in FIG. 26, the same numerals as used in FIG. 25 are usedto denote steps corresponding to those in FIG. 25 for description.

A motor drive direction restricted by a motor drive directionrestricting circuit 25 is estimated from a motor output direction and asteering torque (step S51). Then, an actual motor drive restrictingdirection is input by the motor drive direction restricting circuit 25(step S52) and whether the motor drive restricting direction estimatedat step S51 coincides with the actual motor drive restricting directionor not (step S53).

When they do not coincide with each other, a time elapsed (500 ms) ismeasured by a timer at step S43 and when 500 ms elapsed, an abnormalstate occurrence flag is set (step S45). Then, a motor output is stopped(step S47).

Whereas, when they coincide with each other, whether the abnormal stateoccurrence flag is set or not is checked (step S44), and when theabnormal flag is set, the motor output is stopped at step S47. Whereas,when flag is not set, the 500 ms timer is cleared at step 46 and themotor output is executed at step 48.

With this operation, the abnormal state of the motor drive directionrestricting circuit 25, a motor output from a CPU 22, steering torquesignal and the like can be sensed. Further, the abnormal state can besensed regardless of the state of the motor drive direction restrictingmeans.

As described above, according to this embodiment, since the operation ofthe motor drive direction restricting means is estimated from the stateof the motor drive means and a steering force as well as this operationis compared with the operation executed by the motor drive directionrestricting means and when they do not continuously coincide with eachother longer than a predetermined time, motor drive is stopped, theabnormal state of the motor drive direction restricting means, motoroutput system and steering torque system can be sensed. When theabnormal state occurs, since the motor output is prohibited, safety isimproved.

Embodiment 13

FIG. 27 is a block diagram showing the arrangement of an embodiment 13.In the drawing, the same numerals as used in FIG. 1 and FIG. 6 are usedto denote components corresponding to those in FIG. 1 and FIG. 6 and thedetailed description thereof is omitted.

In this embodiment, a microcomputer 32 (hereinafter, referred to as aCPU 32) is disposed in a controller 2G in place of the aforesaid motordrive direction restricting circuit.

Next, operation will be described with reference to the flowchart ofFIG. 28.

FIG. 28(a) is a flowchart showing the processing executed by a CPU 22 asa first microcomputer and FIG. 28(b) is a flowchart showing theprocessing executed by the CPU 32 as a second microcomputer. Note, inthe drawings, since steps denoted by the same numerals as those of FIG.21 represent the same operation, only different steps will be describedhere.

The CPU 22 inputs a motor drive restricting direction from the CPU 32 atstep S60 and compares at step 26 the motor drive restricting directionwith a motor drive direction determined at step S23.

The CPU 32 inputs a steering torque from a steering torque sensor 1 atstep S61 and also inputs a rightward motor drive direction signal RD1and leftward motor drive signal LD1 from the CPU 22 at step S62. Then,the CPU 32 changes a determined steering torque value in accordance withthe rightward motor drive signal RD1 or leftward motor drive signal LD1at step S63. At step S64, the CPU 32 determines whether the absolutevalue of the steering torque is larger than a determined motor drivedirection value or not, and when the former is larger than the latter,the CPU 32 release the restriction of the motor drive direction (stepS65). Whereas, when the former is equal or smaller than the latter, theCPU 32 restricts the motor drive direction to one direction determinedby the steering torque (step S66).

As described above, according to this embodiment, a motor drivedirection can be restricted only by comparing a steering forcedetermination level with a steering force each corresponding to a motordrive direction and motor drive can be restricted only to a directioncorresponding to the polarity of a steering force. That is, an adverseaffect to steering feeling caused by the motor drive directionrestricting means is removed and excellent steering feeling can beprovided. Further, the safety and reliability of the system is improved.

What is claimed is:
 1. A vehicle control apparatus, comprising:steeringforce sensing means for sensing a steering force; a motor for generatinga steering assisting force; a first microcomputer connected to saidsteering force sensing means for controlling said motor by determining amotor drive direction based on said steering force; and a secondmicrocomputer connected to said steering force sensing means and saidfirst microcomputer for restricting the drive of said motor bydetermining a motor drive restricting direction based on the motor drivedirection of said first microcomputer and at least said steering force,wherein:said second microcomputer includes a means for changing asteering force determination level in accordance with the motor drivedirection of said first microcomputer and a motor drive directionrestricting means for determining said motor drive restricting directionin accordance with the result of comparison of said steering force withsaid steering force determination level; and said motor driverestricting means restricts said motor drive restricting direction inaccordance with the result of a comparison of said steering forcedetermination level with a motor drive direction determined based onsaid steering force.
 2. A vehicle control apparatus according to claim1, wherein phase compensation means is interposed between said steeringforce sensing means and said motor drive direction restricting means. 3.A vehicle control apparatus according to claim 1, wherein said motordrive means includes a bridge circuit composed of at least fourtransistors and said motor drive direction restricting means restrictsoperation with respect to a pair of the transistors of said bridgecircuit.